Hymenoptera venom allergy (HVA) represents a particular risk for exceptionally severe anaphylactic sting reactions in patients with clonal mast cell disorders (CMD). Nevertheless, conventional investigations are not sufficient to do accurate risk assessments. Increased levels of baseline serum tryptase (sBT) (>11.4 μg/L) is highly associated with severe anaphylactic reactions and with a possible underlying CMD. The measurement of baseline serum tryptase, thus, has opened the possibility to screen for CMD. In the present study, we sought to investigate whether bone marrow evaluation provides more accurate diagnosis in patients with HVA.Three patients of the same sex and similar age with HVA were enrolled in this clinical study. The patients underwent comprehensive allergy work-up including skin prick testing, measurements of serum total IgE concentrations and baseline serum tryptase. Bone-marrow biopsies were also performed in all three patients to assess underlying CMD.We evaluated characteristics of the bone marrow mast cells by pathology, flow cytometry and detection of D816V mutation by using current WHO-criteria, which led to changes in the final diagnosis compared to the assessments done by classical allergy work-up and measurements of sBT. Three distinct diagnostic outcomes including systemic mastocytosis, monoclonal mast cell activation syndrome and non-clonal HVA were revealed.We conclude that a bone marrow investigation is required for the correct diagnosis of hymenoptera venom-induced anaphylactic reactions in patients with elevated baseline tryptase levels (>11.4 μg/L), and this has important implications for management strategies.